1. Field of the Invention
The present invention relates generally to a power management apparatus and a method of operating the same, and more particularly to a power management apparatus of a renewable energy generation and a method of operating the same.
2. Description of Prior Art
The development of technologies and economic activities causes rapid energy consumption on the earth so that hidden energy crisis seems to exist. Hence, it is important to save energy as well as develop energy, more particular to the renewable energy. The renewable energy can be used to achieve self-sufficient power supply and further the redundant part thereof can be fed back to the power system to sell power demand back to the power companies.
Take the solar photovoltaic generation system as an example, the solar photovoltaic system provides a photovoltaic conversion to generate a DC power through the solar cell panels. Afterward, the DC power is converted into an AC power through a power conditioner to supply to a load or to the utility grid bus which is grid-connected to an AC utility power. The solar photovoltaic system can be broadly divided into three categories: (1) stand-alone system, (2) grid-connection system, and (3) hybrid system.
The stand-alone system means that the solar photovoltaic system is completely operational without requiring external support and only directly supply to a load. Hence, the stand-alone system is generally built in remote areas or isolated islands. In particular, the required power electricity of a load is either the wind power or the solar power. The solar power or/and the wind power can further provide redundant power to charge the standby battery, whereas the load can be supplied through the battery when the solar power or/and the wind power is insufficient. The grid-connection system means that the solar photovoltaic system is further connected to the power grid of the electric power company. Hence, the grid-connection system is suitable for where the utility power can reach. When the amount of electricity generation of the solar photovoltaic system is greater than that of load demands, the redundant power remains would be delivered to the utility grid bus. On the other hand, the utility power can provide the required power electricity to a load when the amount of electricity generation of the solar photovoltaic system is insufficient. Furthermore, in order to improve the power supply reliability and quality, the hybrid system is developed. The solar photovoltaic system, which is combined with standby batteries, is temporarily separated from the utility power to provide power electricity to a load when the utility power fails. The solar photovoltaic system is further grid-connected to the utility grid bus and charge the standby battery until the utility power is available.
Reference is made to FIG. 1 which is a schematic diagram of a prior art renewable energy generation system. In this generation system structure, electricity generation is determined according to a maximum output power of the renewable energy apparatuses, instead of use conditions of loads, for dispatching power. Hence, it is possible to increase difficulty of the power dispatching and even harm to the system reliability. In addition, it is unable to protect loads once the electrical power system occurs abnormal operation.
Accordingly, it is desirable to provide a power management apparatus and a method of operating the same so that it is to switch the renewable energy generation apparatus in a grid-connection operation or a stand-alone operation by providing an additional switch unit. In addition, a voltage sensor and a current sensor are provided to sense path voltage and path current, respective, so that an electric connection between the AC utility, the renewable energy generation apparatus, and the load is disconnected to protect the load when an abnormal operation is sensed.